1. Field of the Invention
The present invention relates to a camera having a focus control function, a lens apparatus, and a camera system.
2. Description of the Related Art
Conventionally, there has been widely used a camera system which is configured with a camera and an interchangeable lens attachable to the camera and which has a focus control function.
In such a camera system, the camera has a structure described later. In other words, the camera is provided with a communication unit which makes communication with the interchangeable lens, a photometry circuit which measures the amount of incident light passing through the interchangeable lens, and a focusing circuit which measures a distance up to a subject or detecting a focusing state of the interchangeable lens. Further, there are provided a shutter control circuit which exposes a film or an image-pickup element such as CCD for an appropriate time, a film feeding circuit (in the case of a film camera) which performs winding/rewinding of a film, a release button which is operated in order to start an image-taking operation which performs an image-taking preparation operation such as photometry or focusing and exposure, and a camera controller which controls various operations of the camera.
On the other hand, the interchangeable lens is provided with a communication unit which makes communication with the camera, a lens drive circuit which drives a focus lens, a diaphragm drive circuit which drives a diaphragm, and a lens controller which controls various operations of the lens.
Here, the lens drive circuit is configured to operate in response to a reception of a voltage supply from a power supply provided in the camera. Further, there is an interchangeable lens using a vibration type motor which is employed as a drive source which drives the focus lens. In the case where the vibration type motor is employed, a voltage supplied from the camera side is converted into a voltage required for driving the vibration type motor in a DC/DC converter to be supplied to the vibration type motor.
In the case where image-taking is performed using the camera system having the above structure, this camera system is operated along an image-taking sequence described later.
At first, when a camera operator operates the release button, a photometry operation and a focusing operation (image-taking preparation operation) are performed, and a diaphragm drive amount and a focus lens drive amount are operated on the basis of this photometry result and the focusing result. Then, drive commands of the focus lens and the diaphragm and information indicating these drive amounts are transmitted to the lens controller of the interchangeable lens.
The lens controller drives the diaphragm and the focus lens by the drive amounts according to the received information. Here, in the case where the vibration type motor is employed as the drive source of the focus lens, as shown in FIG. 4(A), after the lens controller receives the focus drive command (DC/DCON), it drives the DC/DC converter at first and boosts an output voltage from the camera to a predetermined voltage level. The camera waits for an operation concerning image-taking during this boosting operation.
Thereafter, the vibration type motor is driven by the drive amount according to the information transmitted from the camera controller. Thereby, the focus lens is moved in an optical axis direction and stopped at an in-focus position. The camera performs an opening/closing operation of the shutter so as to expose a film or an image-pickup element for an appropriate time.
As described above, in the case where the vibration type motor is employed as the drive source of the focus lens, the drive of the focus lens has to be waited for only a predetermined time after the focus drive command from the camera controller is received until the output voltage of the DC/DC converter reaches a sufficient voltage level. Therefore, a time loss for the standby time occurs, which causes a long lens drive time after the operator operates the release button until the focus lens reaches the in-focus position.
It is an object of the present invention to provide a camera, a lens apparatus, and a camera system capable of reducing a time after a lens drive command is output until a lens is driven.
In order to achieve the above object, a camera system according to one aspect of the present invention comprises a lens apparatus having a booster circuit which boosts a supply voltage, an actuator which receives a voltage supply from the booster circuit so as to drive a lens unit, and a lens controller which controls the drive of the booster circuit and the actuator. Further, the camera system comprises a camera having a communication unit which makes communication with the lens controller and a camera controller which transmits a lens drive command for driving the actuator to the lens controller via the communication unit.
The camera controller also transmits a booster drive command for driving the booster circuit to the lens controller. Further, the lens controller drives the booster circuit in response to a reception of the booster drive command, and drives the actuator in response to a reception of the lens drive command.
The characteristics of the camera, the lens apparatus, and the camera system according to the present invention will be apparent from the following specific description of an embodiment with reference to the drawings.